Semiconductor laser device and manufacturing method thereof

ABSTRACT

A semiconductor laser device includes an n-type clad layer, a first p-type clad layer and a ridge stripe. The device also includes an active layer interposed between the n-type clad layer and the first p-type clad layer, and a current-blocking layer formed on side surfaces of the ridge stripe. The ridge stripe of the device includes a second p-type clad layer formed into a ridge stripe shape on the opposite surface of the first p-type clad layer from the n-type clad layer. The ridge stripe is formed such that a first ridge width as the width of a surface of the second p-type clad layer exists on the same side as the first p-type clad layer and a second ridge width as the width of a surface of the second p-type clad layer exists on the opposite side from the first p-type clad layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 14/108,165, filed onDec. 16, 2013, which is a Continuation of U.S. application Ser. No.13/359,494, filed on Jan. 26, 2012, and allowed on Aug. 20, 2013, thesubject matter of which is incorporated herein by reference. The parentapplication Ser. No. 13/359,494 is based upon and claims the benefit ofpriority from Japan Patent Application Nos. 2011-15731 and 2011-15732,filed on Jan. 27, 2011, respectively, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure(s) relate to a semiconductor laser device and amanufacturing method thereof.

BACKGROUND

In order to increase a storage capacity of a hard disc drive (HDD),there is a need to record signals in a microscale region of a disc. Forthe purpose of writing signals in the microscale region of a disc whileassuring the stability of the recorded signals in the presence ofthermal changes, it is necessary to use a thermally stable recordingmedium. This however poses a dilemma in that strong magnetic fields arerequired to rewrite the signals. Nowadays, the recording density growssaturated in an up-to-date GMR (Giant Magneto Resistance) method. Thus,there is a need for a “heat-assisted recording” method.

SUMMARY

The present disclosure(s) include some embodiments of a semiconductorlaser device capable of obtaining TM-mode oscillation. Moreover, thepresent disclosure(s) include some embodiments of a semiconductor laserdevice which is suitable for large output purposes and capable ofobtaining stable TM-mode oscillation.

The “heat-assisted recording” method refers to a method in which, usinga laser diode (semiconductor laser device) as a heat source, a force forholding magnetic fields is temporarily weakened and a writing task isperformed in that state. Unlike a conventional semiconductor laserdevice for optical pickup, a semiconductor laser device used in arecording device of “heat-assisted recording” types need to generate alarge output despite its small chip size. Since a restriction is imposedon the mounting space of the semiconductor laser device, it is sometimesnecessary to realize not only TE (Transverse Electric) polarization, butalso TM (Transverse Magnetic) polarization.

According to some embodiments, there is provided a semiconductor laserdevice. The semiconductor laser device includes a p-type clad layer andan n-type clad layer, a p-side guide layer and an n-side guide layer,and an active layer. The p-side guide layer and the n-side guide layerare interposed between the p-type clad layer and the n-type clad layer.The active layer is interposed between the p-side guide layer and then-side guide layer. The active layer includes at least two quantum welllayers and a barrier layer interposed between the quantum well layersadjoining to each other. Each of the p-type clad layer and the n-typeclad layer is formed of a (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer(0≦x1≦1). Each of the p-side guide layer, the n-side guide layer and thebarrier layer is formed of an Al_(x2)Ga_((1−x2))As layer (0≦x2≦1). Eachof the quantum well layers is formed of a GaAs_((1−x3))P_(x3) layer(0≦x3≦1). The (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer has acomposition, where x1>0.7, and the Al_(x2)Ga_((1−x2))As layer having acomposition, where 0.4≦x2≦0.8.

In the configuration of some embodiments, each of the p-type clad layerand the n-type clad layer is formed of a(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer (0≦x1≦1) while each of thep-side guide layer and the n-side guide layer is formed of aAl_(x2)Ga_((1−x2))As layer (0≦x2≦1). It is therefore possible toincrease the band gap difference between the clad layers and the guidelayers. Since the clad layers and the guide layers are formed ofmaterials differing in self-diffusing coefficient from each other, it ispossible to make different the diffusing velocity of carriers in theclad layers and the diffusing velocity of carriers in the guide layers.This makes it possible to prevent the carriers from being excessivelyimplanted into the active layer. As a consequence, it is possible torestrain or prevent occurrence of a so-called carrier overflowphenomenon in which the carriers overflow from the active layer to theclad layers or other surrounding layers in proportion to the rise intemperature. Accordingly, it is possible to restrain or preventdeterioration of characteristics which may be caused by the carrieroverflow phenomenon.

In the configuration of some embodiments, the(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer has a composition, wherex1>0.7, and the Al_(x2)Ga_((1−x2))As layer has a composition, where0.4≦x2≦0.8. The reasons are as follows. The band gaps of the clad layersand the guide layers become greater as the Al composition grows higher.As set forth above, the band gap difference between the guide layers andthe clad layers may be set equal to or greater than a predeterminedvalue to prevent the carriers from being excessively implanted into theactive layer. More specifically, the band gap of the clad layers may beincreased, while the band gap of the guide layers is decreased. The bandgap difference can be made equal to or greater than the predeterminedvalue by setting x1 greater than 0.7 and setting x2 equal to or smallerthan 0.8.

In the semiconductor laser device, a tensile strain may have a latticemismatch rate of not greater than −0.4% and not less than −0.9% begenerated in each of the quantum well layers. If the lattice mismatchrate is greater than −0.4% (if the tensile strain is too small), theoscillation in the TM mode is hard to occur. If the lattice mismatchrate is smaller than −0.9% (if the tensile strain is too large), crystaldefects are generated with ease.

In the semiconductor laser device, the oscillation wavelength may be notless than 780 nm and not greater than 830 nm and that the thickness ofeach of the quantum well layers be not less than 9 nm and not greaterthan 12 nm. If the oscillation wavelength and the thickness of thequantum well layers satisfy the above-noted conditions, it is possibleto keep a TM component light output greater than a TE component lightoutput and to reduce a threshold current.

In the semiconductor laser device, the GaAs_((1−x3))P_(x3) layer mayhave a composition satisfying a condition that a ratio x3/(1−x3) of acomposition x3 of P to a composition (1−x3) of As is not less than 1/9and not greater than ¼. The reasons are as follows. In order to causethe semiconductor laser device to oscillate in the TM mode, it isnecessary that a tensile strain is generated in each of the quantum welllayers. If the lattice constant of the quantum well layers growssmaller, it is possible to generate a greater tensile strain in each ofthe quantum well layers. The lattice constant of the GaAs_((1−x3))P_(x3)layer forming the quantum well layers grows smaller as the ratiox3/(1−x3) of the composition of P to the composition of As becomesgreater. In other words, if the ratio x3/(1−x3) becomes larger, it ispossible to generate a greater tensile strain in each of the quantumwell layers.

The reason for the ratio x3/(1−x3) may be not less than 1/9 is to makethe TM component light output greater than the TE component lightoutput. On the other hand, the reason for the ratio x3/(1−x3) may be notgreater than ¼ is that, if the ratio x3/(1−x3) is greater than ¼, thetensile strain generated in each of the quantum well layers due to theincrease of the P composition becomes greater, which may possiblygenerate a crack and a leak current.

According to some embodiments, each of the quantum well layers has athickness of not less than 9 nm and not greater than 12 nm, the barrierlayer having a thickness smaller than the thickness of each of thequantum well layers. In the semiconductor laser device, the number ofthe quantum well layers may be not less than 2 and not greater than 5.If the number of the quantum well layers is less than 2, there is a needto increase the thickness of one of the quantum well layers. Thus,crystal defects are generated with ease. On the other hand, if thenumber of the quantum well layers is greater than 5, there exist anincreased number of interfaces. Thus, crystal defects are generated withease. In the semiconductor laser device, the p-type clad layer and then-type clad layer may have a carrier concentration of not less than0.7×10¹⁸ cm⁻³ and not greater than 2.0×10¹⁸ cm⁻³. If the carrierconcentration is less than 0.7×10¹⁸ cm⁻³, it becomes difficult toimplant the carriers into the active layer. On the other hand, if thedopant concentration is greater than 2.0×10¹⁸ cm⁻³, the carriers areexcessively implanted into the active layer. The excess carriers becomea light absorbing source, thereby worsening the oscillation efficiency.

In the semiconductor laser device, the end surface window structures forexpanding a band gap of the active layer may be formed in end surfaceportions of a laser resonator. If the end surface window structures areformed in the end surface portions of the laser resonator, it ispossible to expand the band gap of the active layer in the end surfaceportions. Thus, the inductively emitted light generated by therecombination of electrons and positive holes within the active layer ishard to be absorbed in the end surface portions of the laser resonator,which makes it possible to restrain generation of heat. It is thereforepossible to reduce the end-surface optical damage and to acquire a largeoutput.

In the semiconductor laser device, the end surface window structures maybe formed by selectively diffusing impurities into the end surfaceportions of the laser resonator and that a diffusion length of theimpurities from an interface between the n-side guide layer and then-type clad layer toward the n-type clad layer is not less than 400 nmand not greater than 1300 nm. In some embodiments, when the diffusionlength is less than 400 nm, it sometimes becomes difficult to obtain theeffect provided by the end surface window structures. In other alternateembodiments, if the diffusion length is greater than 1300 nm, thediffusion amount of impurities sometimes becomes larger, which maypossibly result in deterioration of the characteristics.

The semiconductor laser device, in some embodiments, includes: an n-typeclad layer; a first p-type clad layer; a ridge stripe including a secondp-type clad layer formed into a ridge stripe shape on the oppositesurface of the first p-type clad layer from the n-type clad layer; anactive layer interposed between the n-type clad layer and the firstp-type clad layer such that a tensile strain is generated in the activelayer; and a current-confining layer formed on the side surfaces of theridge stripe. The ridge stripe is formed such that a first ridge widthas the width of a surface of the second p-type clad layer existing atthe same side as the first p-type clad layer is not less than 3.0 μm andnot greater than 4.5 μm and a second ridge width as the width of asurface of the second p-type clad layer existing at the opposite sidefrom the first p-type clad layer is not less than 2.0 μm. With thisconfiguration, there is provided the active layer in which a tensilestrain is generated. It is therefore possible to obtain a semiconductorlaser device oscillating in the TM mode.

If the first ridge width is too small, carriers tend to concentrate onthe width-wise central region of the semiconductor laser device duringoperation and the current density grows higher. Therefore, a kink isgenerated with ease. On the other hand, if the first ridge width is toolarge, a current diffusing range becomes greater and a carrier supplyshortage occurs during operation. Therefore, a kink is generated withease. Since the first ridge width is set not less than 3.0 μm and notgreater than 4.5 μm, in some embodiments, it is possible to restrain orprevent generation of the kink. Accordingly, it is possible to obtain asemiconductor laser device with stable characteristics.

If the second ridge width is too small, the resistance of the ridgestripe becomes greater. The increase in the resistance of the ridgestripe leads to an increase in an operating current and a decrease in apeak value of the light output. Since the second ridge width is set notless than 2.0 μm, in some embodiments, it is possible to reduce theresistance of the ridge stripe. This makes it possible to lower theoperating current and to prevent the decrease in the peak value of thelight output.

In the semiconductor laser device, the first p-type clad layer may havea thickness of not less than 300 nm and not greater than 400 nm. If thethickness of the first p-type clad layer is smaller than 300 nm, it isdifficult to reduce the refractive index difference between the firstp-type clad layer and the active layer. Thus, a kink is generated withease. On the other hand, if the thickness of the first p-type clad layeris greater than 400 nm, the current flow path extending from the secondp-type clad layer to the active layer becomes longer, therebydeteriorating the characteristics.

In some embodiments, the semiconductor laser device is athree-time-grown semiconductor laser device manufactured by forming ap-type contact layer after the current-blocking layer is formed. Thecurrent-blocking layer is formed of an n-type(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1) layer that has acomposition, where 0.7≦x4≦0.9.

If the Al composition in the n-type(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P layer forming the current-blockinglayer becomes greater, the refractive index of the current-blockinglayer grows smaller. If x4 is smaller than 0.7, the refractive indexdifference between the first and second p-type clad layers and thecurrent-blocking layer becomes smaller. This weakens the lightconfinement effect in the width direction provided by thecurrent-blocking layer. Thus, the operating current grows larger and thepeak output becomes smaller. On the other hand, if x4 is greater than0.9, the refractive index difference between the first and second p-typeclad layers and the current-blocking layer becomes too great. This makestoo strong the light confinement effect in the width direction providedby the current-blocking layer. Thus, the light density is increased andthe kink is generated with ease. In the embodiment set forth above, the(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P layer has a composition, where0.7≦x4≦0.9. It is therefore possible to prevent reduction of the peakoutput and to restrain or prevent generation of the kink. This makes itpossible to obtain a semiconductor laser device which is suitable forlarge output purposes and stable in characteristics.

In the semiconductor laser device, the n-type(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P current-blocking layer may have athickness of not less than 300 nm and not greater than 450 nm. If thethickness of the current-blocking layer is less than 300 nm, it islikely that, when seen in a cross section view, the light beam emitstoward the contact layer beyond the current-blocking layer. On the otherhand, if the thickness of the current-blocking layer is greater than 450nm, it becomes difficult to form the current-blocking layer.

According to some embodiments, the semiconductor laser device is aone-time-grown semiconductor laser manufactured by forming a p-typecontact layer, when forming the second p-type clad layer, and thenforming the current-blocking layer. The current-blocking layer is formedof a SiO₂ layer or a SiN layer. In the semiconductor laser device, thecurrent-blocking layer may have a thickness of not less than 200 nm andnot greater than 300 nm. If the thickness of the current-blocking layeris less than 200 nm, it is likely that, when seen in a cross sectionview, the light beam emits from the current-blocking layer. On the otherhand, if the thickness of the current-blocking layer is greater than 300nm, a stress is generated in the active layer due to the difference inthermal expansion coefficient between the current-blocking layer and theactive layer. This is because the SiO₂ or SiN layer is hard.Consequently, it is likely that the magnitude of the tensile straingenerated in the active layer may undergo a change.

In the semiconductor laser device, the end surface window structures forexpanding a band gap of the active layer may be formed in end surfaceportions of a laser resonator. If the end surface window structures areformed in the end surface portions of the laser resonator, it ispossible to expand the band gap of the active layer in the end surfaceportions. Thus, the inductively emitted light generated by therecombination of electrons and positive holes within the active layer ishard to be absorbed in the end surface portions of the laser resonator,which makes it possible to restrain generation of heat. It is thereforepossible to reduce the end-surface optical damage and to acquire a largeoutput of the device.

In the semiconductor laser device, the n-type clad layer, the firstp-type clad layer and the second p-type clad layer may be formed of a(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer that has a composition,where x1>0.7. The reasons are as follows. The band gaps of the n-typeclad layer, the first p-type clad layer and the second p-type clad layerbecome greater as the Al composition grows higher. The band gapdifference between the guide layers and the clad layers be set equal toor greater than a predetermined value in order for the clad layers tosatisfactorily perform carrier confinement and light confinement. Theband gap difference can be made equal to or greater than thepredetermined value by setting x1 greater than 0.7.

According to some embodiments, there is provided a method ofmanufacturing a semiconductor laser device. The method includes formingan n-type clad layer; forming a first p-type clad layer; forming a ridgestripe including a second p-type clad layer formed into a ridge stripeshape on the opposite surface of the first p-type clad layer from then-type clad layer; forming an active layer interposed between the n-typeclad layer and the first p-type clad layer; and forming acurrent-blocking layer on side surfaces of the ridge stripe. The ridgestripe is formed is configured such that a first ridge width as thewidth of a surface of the second p-type clad layer exists on the sameside as the first p-type clad layer and a second ridge width as thewidth of a surface of the second p-type clad layer exists at theopposite side from the first p-type clad layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view for illustrating a semiconductor laser diodeconfiguration, according to some embodiments.

FIG. 2 is a section view taken along line II-II in FIG. 1.

FIG. 3 is a section view taken along line III-III in FIG. 1.

FIG. 4 is a diagrammatic section view for illustrating a configurationof an active layer of a semiconductor laser diode, according to someembodiments.

FIG. 5 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some embodiments.

FIG. 6 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 7 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 8 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 9 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 10 is a plan view illustrating a manufacturing step of asemiconductor laser diode, according to some embodiments.

FIG. 11 is a plan view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 12 is a plan view for illustrating the configuration of asemiconductor laser diode, according to some other embodiments.

FIG. 13 is a section view taken along line XIII-XIII in FIG. 12.

FIG. 14 is a section view taken along line XIV-XIV in FIG. 12.

FIG. 15 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 16 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 17 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 18 is a section view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 19 is a plan view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

FIG. 20 is a plan view illustrating a manufacturing step of asemiconductor laser diode, according to some other embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. In the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the present invention(s).However, it will be apparent to one of ordinary skill in the art thatthe present invention(s) may be practiced without these specificdetails. In other instances, well-known methods, procedures, systems,and components have not been described in detail so as not tounnecessarily obscure aspects of the various embodiments.

Various embodiments will now be described in detail with reference tothe accompanying drawings. FIG. 1 is a plan view for illustrating aconfiguration of a semiconductor laser diode according to someembodiments. FIG. 2 is a section view taken along line II-II in FIG. 1.FIG. 3 is a section view taken along line III-III in FIG. 1. Thesemiconductor laser diode 70 is a three-time-grown semiconductor laserdiode manufactured through a three-time crystal growing step. Thesemiconductor laser diode 70 is also a Fabry-Perot type semiconductorlaser diode including, as shown in FIGS. 2 and 3, a substrate 1, asemiconductor laminate structure 2 formed on the substrate 1 by crystalgrowth, an n-type electrode 3 formed in contact with the rear surface ofthe substrate 1 (the opposite surface of the substrate 1 from thesemiconductor laminate structure 2) and a p-type electrode 4 formed incontact with the front surface of the semiconductor laminate structure2.

The substrate 1 may be formed of a GaAs monocrystalline substrate, butother types of substrates are possible. The plane direction of the frontsurface of the GaAs substrate 1 has an off-angle of 10 degrees withrespect to a (100) plane. Individual layers that make up thesemiconductor laminate structure 2 are caused to epitaxially grow withrespect to the substrate 1. The term “epitaxial growth” used hereinrefers to crystal growth performed while keeping the continuity oflattices from a ground layer. The mismatch of the lattices with respectto the ground layer is absorbed by the distortion of lattices of acrystal-grown layer, thereby maintaining the continuity of lattices onthe interface with the ground layer.

The semiconductor laminate structure 2 includes an active layer 10, ann-side guide layer 11, a p-side guide layer 12, an n-type semiconductorlayer 13 and a p-type semiconductor layer 14. The n-type semiconductorlayer 13 is arranged between the n-side guide layer 11 and the topsurface of the substrate 1. The n-side guide layer 11 is arrangedbetween the n-type semiconductor layer 13 and the active layer 10.

The p-type semiconductor layer 14 is arranged on the p-side of theactive layer 10 at which the p-type electrode 4 exists. The p-side guidelayer 12 is arranged between the active layer 10 and the p-typesemiconductor layer 14. Thus, there is formed a double hetero-junction.Electrons are implanted into the active layer 10 from the n-typesemiconductor layer 13 via the n-side guide layer 11. Positive holes areimplanted into the active layer 10 from the p-type semiconductor layer14 via the p-side guide layer 12. Light is emitted as the electrons andthe positive holes are recombined in the active layer 10.

The n-type semiconductor layer 13 is formed by laminating an n-type GaAsbuffer layer 15 and an n-type (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P cladlayer (0≦x1≦1) 16 from the front side of the substrate 1. The width ofthe n-type GaAs buffer layer 15 may be one of many possible widths. Forexample, the thickness of the n-type GaAs buffer layer 15 may be 50 nmto 100 nm or may have a thickness of 100 nm. The n-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 16 may also beone of many possible widths, and may, for example, have a thickness of2000 nm to 3000 nm or a thickness of 2500 nm.

The p-type semiconductor layer 14 may be formed by laminating, on thep-type guide layer 12, a first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 17, a p-typeInGaP etching stop layer 18, a second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 19, a p-typeGaAs cap layer 20 and a p-type GaAs contact layer 21. The first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 17 may have athickness of, e.g., 250 nm to 400 nm or a thickness of 300 nm, but otherwidths may be possible. The p-type InGaP etching stop layer 18 may havea thickness of, e.g., 5 nm to 10 nm, or a thickness of 5 nm, but otherwidths may be possible. The second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 19 may have athickness of, e.g., 1000 nm to 1500 nm, or a thickness of 1000 nm, butother widths are possible. The p-type GaAs cap layer 20 may have athickness of, e.g., 50 nm to 100 nm, or a thickness of 100 nm but otherwidths are possible. The p-type GaAs contact layer 21 may have athickness of, e.g., 1000 nm to 2000 nm, or a thickness of 1000 nm butother widths are possible.

The n-type GaAs buffer layer 15 is provided to increase the adhesivenessbetween the GaAs substrate 1 and the n-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer 16. The n-type GaAsbuffer layer 15 may become an n-type semiconductor layer by doping,e.g., utilizing an Si as an n-type dopant, on GaAs. The p-type GaAscontact layer 21 is a low resistance layer for making ohmic contact withthe p-type electrode 4. The p-type GaAs contact layer 21 may become ap-type semiconductor layer by doping, e.g., utilizing Zn as a p-typedopant, on GaAs. It will be appreciated, however, that other dopants maybe utilized.

The n-type clad layer 16 and the first and second p-type clad layers 17and 19 provide a carrier confinement effect by which the carriers(electrons and positive holes) are confined in the active layer 10, anda light confinement effect by which the light coming from the activelayer 10 is confined between the n-type clad layer 16 and the first andsecond p-type clad layers 17 and 19. The n-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer 16 may be converted toan n-type semiconductor layer by doping, e.g., Si as an n-type dopant,on (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P. The first and second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layers 17 and 19 areconverted to p-type semiconductor layers by doping, e.g., Zn as a p-typedopant, on (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P.

The clad layers 16, 17 and 19 may have a dopant concentration of notless than 0.7×10¹⁸ cm⁻³ and not greater than 2.0×10¹⁸ cm⁻³. In someembodiments if the dopant concentration is lower than 0.7×10¹⁸ cm⁻³, itsometimes becomes difficult to implant the carriers into the activelayer 10. In other alternate embodiments, if the dopant concentration ishigher than 2.0×10¹⁸ cm⁻³, the carriers are sometimes excessivelyimplanted into the active layer 10. The excess carriers become a lightabsorbing source, thereby worsening the oscillation efficiency.

In some embodiments, The n-type (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)Pclad layer 16 is wider in band gap than the n-side guide layer 11. Thefirst and second p-type (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P cladlayers 17 and 19 are wider in band gap than the p-side guide layer 12.This makes it possible to perform the carrier confinement and the lightconfinement in an efficient manner and to realize a highly efficientsemiconductor laser diode.

In some embodiments, reducing the end-surface optical damage allows fora large output to be acquired. In light of this, as set forth below, endsurface window structures 40 for expanding the band gap of the activelayer 10 may be formed by diffusing impurities such as zinc, or thelike, into the laser resonator end surface portions. When diffusingimpurities such as zinc, or the like, to form the end surface windowstructures 40, the diffusing velocity becomes faster if phosphorus iscontained in the region to which impurities are to be diffused. In someembodiments, each of the n-type clad layer 16 and the first and secondp-type clad layers 17 and 19 is formed of a(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer containing phosphorus.Accordingly, it becomes easy to diffuse impurities such as zinc, or thelike, which in turn makes it easy to form the end surface windowstructures 40. This makes it possible to realize a semiconductor laserdiode which is suitable for a large output.

The n-type clad layer 16 and the first and second p-type clad layers 17and 19 are lattice-matched with the GaAs substrate 1 because thecomposition ratio of Indium to (Al_(x1)Ga_((1−x1))) is set equal to0.51:0.49. It is therefore possible to obtain high-quality crystals. Asa result, it is possible to obtain a highly reliable semiconductor laserdevice. The n-side guide layer 11 is formed of a Al_(x2)Ga_((1−x2))As(0≦x2≦1) layer (having a thickness of, for example, 20 nm to 30 nm or athickness of 20 nm) and is laminated on the n-type semiconductor layer13. The p-side guide layer 12 is formed of a Al_(x2)Ga_((1−x2))As(0≦x2≦1) layer (having a thickness of, for example, 20 nm to 30 nm or athickness of 20 nm) and is laminated on the active layer 10.

The n-side Al_(x2)Ga_((1−x2))As guide layer 11 and the p-sideAl_(x2)Ga_((1−x2))As guide layer 12 are semiconductor layers that causea light confinement effect to occur in the active layer 10.Additionally, in cooperation with the clad layers 16, 17 and 19, then-side Al_(x2)Ga_((1−x2))As guide layer 11 and the p-sideAl_(x2)Ga_((1−x2))As guide layer 12 form a carrier confinement structurefor blocking carriers within the active layer 10. This makes it possibleto increase the efficiency of recombination of electrons and positiveholes in the active layer 10.

In some embodiments, the clad layers 16, 17 and 19 are formed of(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P (0≦x1≦1) while the guide layers 11and 12 are formed of Al_(x2)Ga_((1−x2))As (0≦x2≦1). It is thereforepossible to increase the band gap difference between the clad layers 16,17 and 19 and the guide layers 11 and 12. It will be appreciated thatother compositions may be utilized to achieve a comparable effect. Sincethe lattice constants of the clad layers 16, 17 and 19 and that of theguide layers 11 and 12 differ from each other, it is possible todifferentiate the diffusing velocity of carriers in the clad layers 16,17 and 19 and the diffusing velocity of carriers in the guide layers 11and 12. This makes it possible to prevent the carriers from beingexcessively implanted into the active layer 10. As a consequence, it ispossible to restrain or prevent occurrence of a so-called carrieroverflow phenomenon in which the carriers overflow from the active layer10 to the clad layers 16, 17 and 19 in proportion to the rise intemperature. Accordingly, it is possible to restrain or preventdeterioration of characteristics which may be caused by the carrieroverflow phenomenon.

The (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer forming each of the cladlayers 16, 17 and 19 may have a composition, where, x1>0.7. TheAl_(x2)Ga_((1−x2))As layer forming each of the guide layers 11 and 12may also have a composition, where 0.4≦x2≦0.8. The reasons are asfollows. The band gaps of the clad layers 16, 17 and 19 and the guidelayers 11 and 12 become greater as the Al composition grows higher. Asset forth above, the band gap difference between the guide layers 11 and12 and the clad layers 16, 17 and 19 may be set equal to or greater thana predetermined value in order to prevent the carriers from beingexcessively implanted into the active layer 10. The band gap differencecan be made equal to or greater than the predetermined value by settingx1 greater than 0.7 and setting x2 equal to or smaller than 0.8.

If the end surface window structures 40 for expanding the band gap ofthe active layer 10 are formed in the laser resonator end surfaceportions, the band gap of the active layer 10 in the laser resonator endsurface portions may become equal to the average value of the band gapof the resonator center portion and the band gap of the guide layers 11and 12. In order to sufficiently expand the band gap of the active layer10 in the end surface portions through the formation of the end surfacewindow structures 40, the band gap of the guide layers 11 and 12 may beconfigured to be equal to or greater than a predetermined value (e.g.,about 1.8 eV). The band gap of the guide layers 11 and 12 can be madeequal to or greater than the predetermined value by setting x2 equal toor greater than 0.4.

In some embodiments, the thickness of the first p-type clad layer 17 maybe not less than 300 nm and not greater than 400 nm. In someembodiments, if the thickness of the first p-type clad layer 17 issmaller than 300 nm, it is sometimes difficult to reduce the refractiveindex difference between the first p-type clad layer 17 and the activelayer 10. Thus, a kink is generated with ease. In other alternateembodiments, if the thickness of the first p-type clad layer 17 isgreater than 400 nm, the current flow path extending from the secondp-type clad layer 19 to the active layer 10 may possibly become longer,thereby deteriorating the characteristics.

The active layer 10 may have a multiple-quantum well-structurecontaining, for example, AlGaAsP. The active layer 10 may be a layer foramplifying a light generated by the recombination of electrons andpositive holes. In some embodiments, as shown in FIG. 4, the activelayer 10 has a multiple-quantum well-structure formed by alternately andrepeatedly laminating, through a plurality of cycles, shown as quantumwell layers 221 and bather layers 222 each containing an undopedAl_(x2)Ga_((1−x2))As layer (0≦x2≦1). In some embodiments, the quantumwell layers 221 have a thickness of, for example, 9 nm to 12 nm or athickness of 12 nm, but other widths are possible. The quantum welllayers 221 also include an undoped GaAs_((1−x3))P_(x3) layer (0≦x3≦1).The bather layers 222 include an undoped Al_(x2)Ga_((1−x2))As layer(0≦x2≦1). The thickness of the barrier layers 222 may be set greaterthan 4 nm but smaller than the thickness of the quantum well layers 221.In some embodiments, the thickness of the barrier layers 222 is 6.5 nmSimilar to the guide layers 11 and 12, the Al_(x2)Ga_((1−x2))As layersforming the barrier layers 222 may have a composition, where 0.4≦x2≦0.8.

Since the lattice constant of the GaAsP layers in an unstrained state issmaller than the lattice constant of the GaAs substrate 1, a tensilestress (or a tensile strain) is generated in each of the quantum welllayers 221 containing the GaAs_((1−x3))P_(x3) layer. This enables thesemiconductor laser diode 70 to oscillate in a TM mode. The lightoutputted in the TM mode becomes a TM wave in which the magnetic fielddirection is perpendicular to the light propagation direction (namely,the electric field direction is parallel to the light propagationdirection).

A tensile strain having a lattice mismatch rate of not greater than−0.4% and not less than −0.9% may be generated in each of the quantumwell layers 221. In some embodiments, if the lattice mismatch rate isgreater than −0.4% (if the tensile strain is small), the oscillation inthe TM mode is sometimes difficult to achieve. In other alternateembodiments, if the lattice mismatch rate is smaller than −0.9% (if thetensile strain is large), crystal defects may sometimes be generatedwith ease. In another alternate embodiment, the oscillation wavelengthmay be not less than 780 nm and not greater than 830 nm, and thethickness of the quantum well layers 221 may be not less than 9 nm andnot greater than 12 nm. If the oscillation wavelength and the thicknessof the quantum well layers 221 satisfy the above-noted conditions, it issometimes possible to keep a TM component light output greater than a TEcomponent light output and to reduce a threshold current.

The GaAs_((1−x3))P_(x3) layer forming the quantum well layers 221 mayhave a composition satisfying the conditions of the ratio x3/(1−x3),where the composition x3 of P to the composition (1−x3) of As is notless than 1/9 and not greater than ¼. The reasons are as follows. Inorder to cause the semiconductor laser diode 70 to oscillate in the TMmode, a tensile strain may be generated in each of the quantum welllayers 221. If the lattice constant of the quantum well layers 221 growssmaller, it is possible to generate a greater tensile strain in each ofthe quantum well layers 221. The lattice constant of theGaAs_((1−x3))P_(x3) layer forming the quantum well layers 221 growssmaller as the ratio x3/(1−x3) of the composition of P to thecomposition of As becomes greater. In other words, if the ratiox3/(1−x3) becomes larger, it is possible to generate a greater tensilestrain in each of the quantum well layers 221.

The reason for the ratio x3/(1−x3) being not less than 1/9 is toincrease the ratio of the TM component light output to the TE componentlight output. The reason for the ratio x3/(1−x3) being not greater than¼ is that, if the ratio x3/(1−x3) is greater than ¼, the tensile straingenerated in each of the quantum well layers 221 due to the increase ofthe P composition becomes greater, which may possibly generate a crackand a leak current.

The number of the quantum well layers 221 may be not less than 2 and notgreater than 5. If the number of the quantum well layers 221 is lessthan 2, the thickness of one of the quantum well layers 221 may beadjusted. Thus, crystal defects are generated with ease. On the otherhand, if the number of the quantum well layers 221 is greater than 5,there exist an increased number of interfaces. Thus, crystal defects aregenerated with ease. As shown in FIG. 3, a ridge stripe 30 may be formedby partially removing the second p-type clad layer 19 and the p-type caplayer 20 existing within the p-type semiconductor layer 14. Morespecifically, the second p-type clad layer 19 and the p-type cap layer20 are partially etched away to form a ridge stripe 30 having asubstantially trapezoidal shape (mesa shape) when seen in a crosssection view. In other words, the ridge stripe 30 is formed of thesecond p-type clad layer 19 and the p-type cap layer 20. The width ofthe surface of the second p-type clad layer 19 existing at the same sideas the first p-type clad layer 17 (the first ridge width) will bereferred to as “ridge bottom width W1”. The width of the surface of thesecond p-type clad layer 19 existing at the opposite side from the firstp-type clad layer 17 (the second ridge width) will be referred to as“ridge top width W2”.

In some embodiments, the ridge bottom width W1 is not less than 3.0 μmand not greater than 4.5 μm, and, more specifically, equal to 3.5 μm. Ifthe ridge bottom width W1 is less than 3.0 μm, carriers tend toconcentrate on the width-wise central region of the semiconductor laserdiode 70 during operation and the current density grows higher.Therefore, a kink is generated with ease. On the other hand, if theridge bottom width W1 is greater than 4.5 μm, a current diffusing rangebecomes greater and a carrier supply shortage occurs during operation.Therefore, a kink is generated with ease. Since the ridge bottom widthW1 is set not less than 3.0 μm and not greater than 4.5 μm, in someembodiments, it is possible to restrain or prevent generation of thekink. Accordingly, it is possible to obtain a semiconductor laser devicewith stable characteristics.

In some embodiments, the ridge top width W2 is not less than 2.0 μm, andmore specifically, equal to 2.5 μm. If the ridge top width W2 is lessthan 2.0 μm, the resistance of the ridge stripe 30 becomes greater. Theincrease in the resistance of the ridge stripe 30 leads to an increasein an operating current and a decrease in a peak value of the lightoutput. Since the ridge top width W2 is set not less than 2.0 μm, it ispossible to reduce the resistance of the ridge stripe 30. This makes itpossible to lower the operating current and to prevent the decrease inthe peak value of the light output.

On the side surface of the ridge stripe 30, there is formed an n-type(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1) current-blocking layer(current-embedding layer) 6, which may have a thickness of 300 nm to 450nm or a thickness of 400 nm, for example. More specifically, the sidesurfaces of the p-type cap layer 20, the exposed surfaces of the secondp-type clad layer 19 and the exposed surfaces of the p-type etching stoplayer 18 are covered with the n-type AlGaInP current-blocking layer 6 inan intermediate region other than the opposite end regions near theopposite end surfaces 31 and 32, as shown in FIG. 2. In someembodiments, the top and side surfaces of the p-type cap layer 20, theexposed surfaces of the second p-type clad layer 19 and the exposedsurfaces of the p-type etching stop layer 18 are covered with the n-typeAlGaInP current-blocking layer 6 in the opposite end regions, as shownin FIGS. 2 and 3. The n-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)Pcurrent-blocking layer 6 becomes an n-type semiconductor layer bydoping, e.g., utilizing Si as an n-type dopant, on(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P.

In the intermediate region, the exposed surfaces of the n-typecurrent-blocking layer 6 and the p-type cap layer 20 are covered withthe contact layer 21. In the opposite end regions, the exposed surfacesof the n-type current-blocking layer 6 are covered with the contactlayer 21. The n-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1)layer forming the current-blocking layer 6 may have a composition, where0.7≦x4≦0.9. The reasons are as follows. If the Al composition in then-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1) layer forming thecurrent-blocking layer 6 becomes greater, the refractive index of thecurrent-blocking layer 6 grows smaller. If x4 is smaller than 0.7, therefractive index difference between the first and second p-type cladlayers 17 and 19 and the current-blocking layer 6 becomes smaller. Thisweakens the light confinement effect in the width direction provided bythe current-blocking layer 6. Thus, the operating current grows largerand the peak output becomes smaller. On the other hand, if x4 is greaterthan 0.9, the refractive index difference between the first and secondp-type clad layers 17 and 19 and the current-blocking layer 6 becomestoo great. This makes too strong the light confinement effect in thewidth direction provided by the current-blocking layer 6. Thus, thelight density is increased and the kink is generated with ease.

In some embodiments, the n-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)Player forming the current-blocking layer 6 has a composition, where0.7≦x4≦0.9. It is therefore possible to prevent reduction of the peakoutput and to restrain or prevent generation of a kink. This makes itpossible to obtain a semiconductor laser device which is suitable forhigh output and stable characteristics. In some embodiments, thethickness of the current-blocking layer 6 may be not less than 300 nmand not greater than 450 nm. If the thickness of the current-blockinglayer 6 is less than 300 nm, it is likely that, when seen in a crosssection view, the light beam emits toward the contact layer 21 beyondthe current-blocking layer 6. On the other hand, if the thickness of thecurrent-blocking layer 6 is greater than 450 nm, it becomes difficult toform the current-blocking layer 6. The semiconductor laminate structure2 may have a pair of end surfaces (cleavage surfaces) 31 and 32 formedof the longitudinal opposite cleavage surfaces of the ridge stripe 30.The end surfaces 31 and 32 may be parallel to each other. Thus, then-side guide layer 11, the active layer 10 and the p-side guide layer 12make up a Fabry-Perot resonator in which the end surfaces 31 and 32 areused as resonator end surfaces. In other words, the light generated inthe active layer 10 is amplified by inductive emission while travelingbetween the resonator end surfaces 31 and 32. The light thus amplifiedis partially emitted, as laser light, from the resonator end surfaces 31and 32 to the outside of the semiconductor laser device.

The n-type electrode 3 may be made of, for example, an AuGe/Ni/Ti/Aualloy, and may be ohmic-joined to the substrate 1 so that the AuGe sidethereof can be positioned at the rear side of the substrate 1. Thep-type electrode 4 may be made of, for example, a Ti/Au alloy, and maybe ohmic-joined to the p-type contact layer 21 so that the Ti sidethereof can be positioned on the p-type contact layer 21. As shown inFIGS. 1 and 2, the end surface window structures 40 for expanding theband gap of the active layer 10 may be formed in the end surfaceportions of the resonator. The end surface window structures 40 may beformed by, for example, diffusing zinc (Zn) into the resonator endsurface portions. The diffusion length L of zinc from the interfacebetween the n-side guide layer 11 and the n-type clad layer 16 towardthe n-type clad layer 16 may be not less than 400 nm and not greaterthan 1300 nm. In some embodiments, if the diffusion length L is lessthan 400 nm, it sometimes becomes difficult to obtain the effectprovided by the end surface window structures. In other alternateembodiments, if the diffusion length L is greater than 1300 nm, thediffusion amount of impurities (zinc in this case) sometimes becomeslarger, which may possibly result in deterioration of characteristics.

With the configuration described above, the n-type electrode 3 and thep-type electrode 4 are connected to a power source. Electrons andpositive holes are implanted from the n type semiconductor layer 13 andthe p-type semiconductor layer 14 into the active layer 10, whereby theelectrons and the positive holes are recombined within the active layer10. This makes it possible to generate light having an oscillationwavelength of, e.g., not less than 780 nm and not greater than 830 nm,but other wavelengths are possible. The light is amplified by inductiveemission while repeating traveling between the resonator end surfaces 31and 32 along the guide layers 11 and 12. Then, a greater laser output istaken out from the resonator end surface 31 as a laser emitting surface.

FIGS. 5 through 11 are horizontal section views showing a manufacturingmethod of the semiconductor laser diode 70 shown in FIGS. 1 through 3.FIGS. 5, 7, 8 and 9 are horizontal section views of the central portion,which correspond to FIG. 3. FIG. 6 is a horizontal section view of theportion near the opposite ends. FIGS. 10 and 11 are plan views.

As shown in FIG. 5, an n-type GaAs buffer layer 15, an n-type(Al_(x1)Ga_(1−x1)))_(0.51)In_(0.49)P clad layer 16, an n-sideAl_(x2)Ga_((1−x2))As guide layer 11, an active layer 10, a p-sideAl_(x2)Ga_((1−x2))As guide layer 12, a first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer 17, a p-type InGaPetching stop layer 18, a second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer 19 and a p-type GaAscap layer 20 may be grown on a GaAs substrate 1 one after another byMOCVD (metal organic chemical vapor deposition) (a first crystal growthstep). The active layer 10 is formed by causing quantum well layers 221each including a GaAs_((1−x3))P_(x3) layer and barrier layers 222 eachincluding a Al_(x2)Ga_((1−x2))As layer to alternately and repeatedlygrow through a plurality of cycles.

Next, as shown in FIGS. 6 and 10, a ZnO (zinc oxide) layer 51 may bepatterned on the p-type GaAs cap layer 20 in the regions near the endsurfaces of the semiconductor laser diode 70. Then, Zn is diffused intothe regions near the end surfaces of the semiconductor laser diode 70by, for example, performing an annealing treatment for about two hoursat a temperature of 500 to 600 degrees Celsius. At this time, theannealing treatment may be performed such that the diffusion length L ofZn from the interface between the n-side guide layer 11 and the n-typeclad layer 16 toward the n-type clad layer 16 falls within a range offrom 400 nm to 1300 nm. Thus, end surface window structures 40 can beformed in the regions near the end surfaces of the semiconductor laserdiode 70.

Next, the ZnO layer 51 may be removed. Subsequently, as shown in FIGS. 7and 11, the p-type cap layer 20 and the second p-type clad layer 19 maybe partially removed through an etching step in which a stripe-shapedSiO₂ insulation film is used as a mask layer 52. Thus, a ridge stripe 30having the mask layer 52 on the top surface thereof may be formed. Afterforming the ridge stripe 30, only the portions 52 a (see FIG. 11) of themask layer 52 existing in the regions near the end surfaces of thesemiconductor laser diode 70 may be removed.

Next, as shown in FIG. 8, an n-type(Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P current-blocking layer 6 may beformed on the surface of the ridge stripe 30 (a second crystal growthstep). At this time, the mask layer 52 serves as a mask. For thatreason, as shown in FIG. 8, the top surface of the ridge stripe 30 (theupper surface of the p-type cap layer 20) may not covered with then-type current-blocking layer 6 in the region corresponding to theintermediate portion between the opposite end portions of thesemiconductor laser diode 70. Since the mask layer 52 does not exist inthe regions near the end surfaces of the semiconductor laser diode 70,the top surface of the ridge stripe 30 (the upper surface of the p-typecap layer 20) may be covered with the n-type current-blocking layer 6 inthe regions near the end surfaces of the semiconductor laser diode 70.

Thereafter, the mask layer 52 may be removed. Then, as shown in FIG. 9,a p-type GaAs contact layer 21 may be grown on the surfaces of then-type current-blocking layer 6 and the p-type cap layer 20 (a thirdcrystal growth step). Finally, a p-type electrode 4 making ohmic contactwith the p-type GaAs contact layer 21 may be formed and an n-typeelectrode 3 making ohmic contact with the GaAs substrate 1 may beformed.

Next, description will be made on the relationship between the tensilestrain amount [%] and the polarization ratio [dB] of the quantum welllayers 221. In this regard, the polarization ratio may be represented byan equation: polarization ratio=10 LOG (TM component light output/TEcomponent light output).

The polarization ratio may be determined utilizing any combination ofparameters. For illustration purposes, the following four scenarios areprovided:

a: semiconductor laser device including an active layer 10, the quantumwell layers 221 having a thickness from 9 nm to 12 nm, and anoscillation wavelength from 820 nm to 830 nm;

b: semiconductor laser device including an active layer 10, the quantumwell layers 221 having a thickness from 9 nm to 12 nm, and anoscillation wavelength from 800 nm to 820 nm;

c: semiconductor laser device including an active layer 10, the quantumwell layers 221 having a thickness from 9 nm to 12 nm, and anoscillation wavelength from 790 nm to 800 nm; and

d: semiconductor laser device including an active layer 10, the quantumwell layers 221 having a thickness from 9 nm to 12 nm, and anoscillation wavelength from 780 nm to 790 nm. The absolute values of thetensile strain amounts [%] of the active layers 10 for the samplescenarios are a<b<c<d. In other words, the tensile strain of sample a issmallest and the tensile strain of sample d is greatest.

Additionally, the conducting condition may be 60 mW at 25 degreesCelsius. The measurement results of polarization ratios [dB] withrespect to samples a through d are shown in Table 1. When the tensilestrain amount [%] of the quantum well layers 221 is zero, thepolarization ratio [dB] is approximately −35.

TABLE 1 Sample Polarization Ratio [dB] a 8 b 25 c 25 d 26

It can be noted from Table 1 that the polarization ratios [dB] of allthe samples are positive and further that the TM component light outputis greater than the TE component light output in all the samples. Thefollowing section below describes the relationship between the tensilestrain amount [%] of the active layer 10 and the threshold current [mA].Using the same sample scenarios a through d above, and a conductingcondition at 25 degrees Celsius, the measurements of threshold currents[mA] with respect to samples a through d are shown in Table 2. When thetensile strain amount [%] of the quantum well layers 221 is zero, thethreshold current [mA] is approximately 24.5 mA.

TABLE 2 Sample Threshold Current [mA] a 21 b 18.9 c 17 d 18.2

It can be noted in Table 2 that the threshold currents [mA] of all thesamples are lower than the threshold current available when the tensilestrain amount [%] is zero. These results reveal that, in someembodiments, if the thickness of the quantum well layers 221 is not lessthan 9 nm and not greater than 12 nm with the oscillation wavelengthbeing not less than 780 nm and not greater than 830 nm, the TM componentlight output becomes greater than the TE component light output and thethreshold current can be kept low.

FIG. 12 is a plan view for illustrating the configuration of asemiconductor laser diode according some embodiments. FIG. 13 is asection view taken along line XIII-XIII in FIG. 12. FIG. 14 is a sectionview taken along line XIV-XIV in FIG. 12. In FIGS. 12 through 14, theportions corresponding to the respective portions shown in FIGS. 1through 3 are designated by the same reference numerals as used in FIGS.1 through 3.

In some embodiments, the semiconductor laser diode 80 may be aone-time-grown semiconductor laser diode manufactured through a one-timecrystal growth step. For example, the semiconductor laser diode 80 is aFabry-Perot type semiconductor laser diode including a substrate 1, asemiconductor laminate structure 2A formed on the substrate 1 by crystalgrowth, an n-type electrode 3 formed in contact with the rear surface ofthe substrate 1 (the opposite surface of the substrate 1 from thesemiconductor laminate structure 2A) and a p-type electrode 4 formed incontact with the front surface of the semiconductor laminate structure2A.

In some embodiments, the substrate 1 is formed of a GaAs monocrystallinesubstrate. The plane direction of the front surface of the GaAssubstrate 1 has an off-angle of 10 degrees with respect to a (100)plane. Individual layers making up the semiconductor laminate structure2A are caused to epitaxially grow with respect to the substrate 1.

The semiconductor laminate structure 2A includes an active layer 10, ann-side guide layer 11, a p-side guide layer 12, an n-type semiconductorlayer 13 and a p-type semiconductor layer 14A. The n-type semiconductorlayer 13 is arranged on the substrate 1 facing the active layer 10. Thep-type semiconductor layer 14A is arranged between the active layer 10and the p-type electrode 4. The n-side guide layer 11 is arrangedbetween the n-type semiconductor layer 13 and the active layer 10. Thep-side guide layer 12 is arranged between the active layer 10 and thep-type semiconductor layer 14A. Thus, there is formed a doublehetero-junction. Electrons are implanted into the active layer 10 fromthe n-type semiconductor layer 13 via the n-side guide layer 11.Positive holes are implanted into the active layer 10 from the p-typesemiconductor layer 14A via the p-side guide layer 12. Light is emittedas the electrons and the positive holes are recombined in the activelayer 10.

The n-type semiconductor layer 13 is formed by laminating an n-type GaAsbuffer layer 15 and an n-type (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P cladlayer (0≦x1≦1) 16 in the named order from the side of the substrate 1.The n-type GaAs buffer layer 15 has a thickness of, for example, 50 nmto 100 nm or a thickness of 100 nm. The n-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 16 has athickness of, for example, 2000 nm to 3000 nm or a thickness of 2500 nm.On the other hand, the p-type semiconductor layer 14A may be formed bylaminating, on the p-type guide layer 12, a first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 17, a p-typeInGaP etching stop layer 18, a second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 19, and ap-type GaAs contact layer 21A. The first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 17 has athickness of, for example, 250 nm to 400 nm or a thickness of 350 nm.The p-type InGaP etching stop layer 18 has a thickness of, for example,5 nm to 10 nm or a thickness of 5 nm. The second p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer (0≦x1≦1) 19 has athickness of, for example, 1000 nm to 1500 nm or a thickness of 1000 nm.The p-type GaAs contact layer 21A has a thickness of, for example, 100nm to 300 nm or a thickness of 300 nm.

The n-side guide layer 11 may be formed of a Al_(x2)Ga_((1−x2))As(0≦x2≦1) layer (having a thickness of, e.g., 20 nm to 30 nm, or athickness of 20 nm) and is laminated on the n-type semiconductor layer13. The p-side guide layer 12 is formed of a Al_(x2)Ga_((1−x2))As(0≦x2≦1) layer (having a thickness of, e.g., 20 nm to 30 nm, or athickness of 20 nm) and is laminated on the active layer 10.

The (Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer forming each of the cladlayers 16, 17 and 19 may have a composition, where x1>0.7. The reasonsare as follows. The band gaps of the clad layers 16, 17 and 19 maybecome greater as the Al composition grows higher. As set forth above,the band gap difference between the guide layers 11 and 12 and the cladlayers 16, 17 and 19 may be set equal to or greater than a predeterminedvalue in order for the clad layers 16, 17 and 19 to satisfactorilyperform carrier blocking and light confinement. The band gap differencecan be made equal to or greater than the predetermined value by settingx1 greater than 0.7.

The thickness of the first p-type clad layer 17 may be not less than 300nm and not greater than 400 nm not to generate a kink easily. If thethickness of the first p-type clad layer 17 is smaller than 300 nm, itis impossible to reduce the refractive index difference between thefirst p-type clad layer 17 and the active layer 10. On the other hand,if the thickness of the first p-type clad layer 17 is greater than 400nm, the current flow path extending from the second p-type clad layer 19to the active layer 10 becomes longer, thereby deteriorating thecharacteristics.

The active layer 10 has a multiple-quantum well structure containing,e.g., AlGaAsP. In some embodiments, as shown in FIG. 4, the active layer10 has a multiple-quantum well structure formed by alternately andrepeatedly laminating, through a plurality of cycles, quantum welllayers 221 and barrier layers 222. The quantum well layers 221 have athickness of, for example, 8 nm to 14 nm or a thickness of 13 nm, andmay include undoped GaAs_((1−x3))P_(x3) layers (0≦x3≦1). The barrierlayers 222 may include undoped Al_(x2)Ga_((1−x2))As layers (0≦x2≦1). Thethickness of the barrier layers 222 may be set greater than 4 nm butsmaller than the thickness of the quantum well layers 221. In someembodiments, the thickness of the barrier layers 222 is 6.5 nm.

Since the lattice constant of the GaAsP layers in an unstrained state issmaller than the lattice constant of the GaAs substrate 1, a tensilestress (or a tensile strain) is generated in each of the quantum welllayers 221 including the GaAs_((1−x3)Px3) layer. This enables thesemiconductor laser diode 80 to oscillate in a TM mode. The lightoutputted in the TM mode becomes a TM wave in which the magnetic fielddirection is perpendicular to the light propagation direction. Namely,the electric field direction is parallel to the light propagationdirection.

A ridge stripe 30A is formed by partially removing the second p-typeclad layer 19 and the p-type contact layer 21A existing within thep-type semiconductor layer 14A. More specifically, the second p-typeclad layer 19 and the p-type contact layer 21A may be partially etchedaway to form a ridge stripe 30A having a substantially trapezoidal shape(mesa shape) when seen in a cross section view. In other words, theridge stripe 30A may be formed of the second p-type clad layer 19 andthe p-type contact layer 21A. The width of the surface of the secondp-type clad layer 19 existing at the same side as the first p-type cladlayer 17 (the first ridge width) will be referred to as “ridge bottomwidth W1”. The width of the surface of the second p-type clad layer 19existing at the opposite side from the first p-type clad layer 17 (thesecond ridge width) will be referred to as “ridge top width ”.

In some embodiments, the ridge bottom width 1 is not less than 3.0 μmand not greater than 4.5 μm, and more specifically, equal to 3.5 μm. Ifthe ridge bottom width W1 is less than 3.0 nm, carriers tend toconcentrate on the width-wise central region of the semiconductor laserdiode 80 during operation and the current density grows higher. Theincrease in the current density causes sudden current implantation,which may possibly generate a kink. On the other hand, if the ridgebottom width W1 is greater than 4.5 μm, a current diffusing rangebecomes greater during operation. The increase in the current diffusingrange leads to carrier shortage, which may possibly generate a kink.Since the ridge bottom width W1 is set not less than 3.0 μm and notgreater than 4.5 μm, in some embodiments, it is possible to restrain orprevent generation of the kink. Accordingly, it is possible to obtain asemiconductor laser device with stable characteristics.

The ridge top width W2 is not less than 2.0 μm, and more specifically,equal to 2.5 μm. If the ridge top width W2 is less than 2.0 μm, theresistance of the ridge stripe 30A becomes greater. The increase in theresistance of the ridge stripe 30A leads to an increase in an operatingcurrent and a decrease in a peak value of the light output. Since theridge top width W2 is set not less than 2.0 μm, in some embodiments, itis possible to reduce the resistance of the ridge stripe 30A. This makesit possible to lower the operating current and to prevent the decreasein the peak value of the light output.

On the side surface of the ridge stripe 30A, there is formed acurrent-blocking layer (embedding layer) 6A, which has a thickness of,e.g., 200 nm to 300 nm, or a thickness of 250 nm and contains a SiO₂ orSiN insulation layer. More specifically, the side surfaces of the p-typecontact layer 21A, the exposed surfaces of the second p-type clad layer19 and the exposed surfaces of the p-type etching stop layer 18 may becovered with the current-blocking layer 6A.

The thickness of the current-blocking layer 6A may be not less than 200nm and not greater than 300 nm. If the thickness of the current-blockinglayer 6A is less than 200 nm, it is likely that, when seen in a crosssection view, the light beam emits from the current-blocking layer 6A.On the other hand, if the thickness of the current-blocking layer 6A isgreater than 300 nm, a stress is generated in the active layer 10 due tothe difference in thermal expansion coefficient between thecurrent-blocking layer 6A and the active layer 10. This is because theSiO₂ or SiN insulation layer is hard. Consequently, it is likely thatthe magnitude of the tensile strain generated in the active layer 10 mayundergo a change.

In some embodiments, the semiconductor laminate structure 2A has a pairof end surfaces (cleavage surfaces) 31 and 32 formed of the longitudinalopposite cleavage surfaces of the ridge stripe 30A. The end surfaces 31and 32 are parallel to each other. Thus, the n-side guide layer 11, theactive layer 10 and the p-side guide layer 12 make up a Fabry-Perotresonator in which the end surfaces 31 and 32 are used as resonator endsurfaces. In other words, the light generated in the active layer 10 isamplified by inductive emission while repeating traveling between theresonator end surfaces 31 and 32. The light thus amplified is partiallyemitted, as laser light, from the resonator end surfaces 31 and 32 tothe outside of the semiconductor laser device.

The n-type electrode 3 may be made of, e.g., an AuGe/Ni/Ti/Au alloy, andis ohmic-joined to the substrate 1 so that the AuGe side thereof can bepositioned at the rear side of the substrate 1. But other substitutematerials may be possible. The p-type electrode 4 may be made of, e.g.,a Ti/Au alloy, and is ohmic-joined to the p-type contact layer 21A sothat the Ti side thereof can be positioned on the p-type contact layer21A. Again, other substitute materials may be possible. As shown inFIGS. 12 and 13, the end surface window structures 40 for expanding theband gap of the active layer 10 may be formed in the end surfaceportions of the resonator. The end surface window structures 40 may beformed by, e.g., diffusing zinc (Zn) into the resonator end surfaceportions.

With the configuration described above, the n-type electrode 3 and thep-type electrode 4 are connected to a power source. Electrons andpositive holes are implanted from the n type semiconductor layer 13 andthe p-type semiconductor layer 14A into the active layer 10, whereby theelectrons and the positive holes are recombined within the active layer10. This makes it possible to generate light having an oscillationwavelength of, e.g., not less than 770 nm and not greater than 830 nm.The light is amplified by inductive emission while repeating travelingbetween the resonator end surfaces 31 and 32 along the guide layers 11and 12. Then, a greater laser output is taken out from the resonator endsurface 31 as a laser emitting surface.

FIGS. 15 through 20 are horizontal section views showing a manufacturingmethod of the semiconductor laser diode 80 shown in FIGS. 12 through 14,according to some embodiments. FIGS. 15, 17 and 18 are horizontalsection views of the central portion, which correspond to FIG. 4. FIG.16 is a horizontal section view of the portion near the opposite ends.FIGS. 19 and 20 are plan views. First, as shown in FIG. 15, an n-typeGaAs buffer layer 15, an n-type (Al_(x1)Ga_((1−x1)))_(0.51) In_(0.49)Pclad layer 16, an n-side Al_(x2)Ga_((1−x2))As guide layer 11, an activelayer 10, a p-side Al_(x2)Ga_((1−x2))As guide layer 12, a first p-type(Al_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P clad layer 17, a p-type InGaPetching stop layer 18, a second p-type(Al_(x1)Ga_(1−x1)))_(0.51)In_(0.49)P clad layer 19 and a p-type GaAscontact layer 21A may be grown on a GaAs substrate 1 one after anotherby metal organic chemical vapor deposition. The active layer 10 may beformed by causing quantum well layers 221 each including aGaAs_((1−x3))P_(x3) layer and barrier layers 222 each including aAl_(x2)Ga_((1−x2))As layer to alternately and repeatedly grow through aplurality of cycles.

Next, as shown in FIGS. 16 and 19, a ZnO (zinc oxide) layer 51 may bepatterned on the p-type GaAs contact layer 21A in the regions near theends of the semiconductor laser diode 80. Then, Zn is diffused into theregions near the end surfaces of the semiconductor laser diode 80 by,e.g., performing an annealing treatment for about two hours at atemperature of 500 to 600 degrees Celsius. Thus, end surface windowstructures 40 may be formed in the regions near the end surfaces of thesemiconductor laser diode 80.

Next, the ZnO layer 51 is removed. Subsequently in some embodiments, asshown in FIGS. 17 and 20, the p-type contact layer 21A and the secondp-type clad layer 19 are partially removed through an etching step inwhich a stripe-shaped SiO₂ insulation film is used as a mask layer 52.Thus, a ridge stripe 30A having the mask layer 52 on the top surfacethereof may be formed. Thereafter, the mask layer 52 is removed. Next,an n-type current-blocking layer 6A containing a SiO₂ or SiN insulationlayer is formed on the surface of the ridge stripe 30A. Thereafter, thecurrent-blocking layer 6A on the p-type contact layer 21A is removed.Thus, as shown in FIG. 18, the side surfaces of the ridge stripe 30A arecovered with the current-blocking layer 6A but the top surface of theridge stripe 30A (the upper surface of the p-type contact layer 21A) maynot be covered with the current-blocking layer 6A.

Finally, a p-type electrode 4 making ohmic contact with the p-type GaAscontact layer 21A may be formed and an n-type electrode 3 making ohmiccontact with the GaAs substrate 1 may be formed.

The present disclosure(s) may be modified in many different formswithout departing from the scope thereof defined in the claims.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the novel devices described herein maybe embodied in a variety of other forms and may be combined;furthermore, various omissions, substitutions and changes in the form ofthe embodiments described herein may be made without departing from thespirit of the disclosures. The accompanying claims and their equivalentsare intended to cover such forms or modifications as would fall withinthe scope and spirit of the disclosures.

What is claimed is:
 1. A semiconductor laser device comprising: ann-type clad layer; a first p-type clad layer; a ridge stripe including asecond p-type clad layer formed into a ridge stripe shape on theopposite surface of the first p-type clad layer from the n-type cladlayer; an active layer interposed between the n-type clad layer and thefirst p-type clad layer; and a current-blocking layer formed on sidesurfaces of the ridge stripe, wherein a first ridge width of a surfaceof the second p-type clad layer existing on the same side as the firstp-type clad layers is greater than or equal to 3.0 μm and less than orequal to 4.5 μm, and a second ridge width of a surface of the secondp-type clad layer existing at the opposite side from the first p-typeclad layer is greater than or equal to 2.0 μm, wherein the semiconductorlaser device is a three-time-grown semiconductor laser devicemanufactured by forming a p-type contact layer after thecurrent-blocking layer is formed, wherein the current-blocking layer isformed of an n-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1) layerthat has a composition satisfying an inequality, 0.7≦x4≦0.9 and whereinthe n-type clad layer, the first p-type clad layer and the second p-typeclad layer are formed of a Al_(x1)Ga _((1−x1)))_(0.51)In_(0.49)P layerthat has a composition where x1>0.7.
 2. The device of claim 1, whereinthe current-blocking layer has a thickness of not less than 300 nm andnot greater than 450 nm.
 3. The device of claim 1, wherein the firstp-type clad layer has a thickness of not less than 300 nm and notgreater than 400 nm.
 4. The device of claim 1, wherein one or more endsurface window structures for expanding a band gap of the active layerare formed in one or more end surface portions of a laser resonator. 5.The device of claim 1, wherein the active layer includes aGaAs_((1−x3))P_(x3) well layer, where 1/9≦x3/(1−x3)≦¼.
 6. Asemiconductor laser device, comprising: an n-type clad layer; a firstp-type clad layer; a ridge stripe including a second p-type clad layerformed into a ridge stripe shape on the opposite surface of the firstp-type clad layer from the n-type clad layer; an active layer interposedbetween the n-type clad layer and the first p-type clad layer; and acurrent-blocking layer formed on side surfaces of the ridge stripe,wherein a first ridge width of a surface of the second p-type clad layerexisting on the same side as the first p-type clad layers is greaterthan or equal to 3.0 μm and less than or equal to 4.5 μm, and a secondridge width of a surface of the second p-type clad layer existing at theopposite side from the first p-type clad layer is greater than or equalto 2.0 μm, wherein the semiconductor laser device is a one-time-grownsemiconductor laser manufactured by forming a p-type contact layer, whenforming the second p-type clad layer, and then forming thecurrent-blocking layer, wherein the current-blocking layer is formed ofa SiO₂ layer or a SiN layer, and the current-blocking layer has athickness of greater than or equal to 200 nm and less than or equal to300 nm, and wherein the n-type clad layer, the first p-type clad layerand the second p-type clad layer are formed of aAl_(x1)Ga_((1−x1)))_(0.51)In_(0.49)P layer that has a composition wherex1>0.7.
 7. The device of claim 6, wherein one or more end surface windowstructures for expanding a band gap of the active layer are formed inone or more end surface portions of a laser resonator.
 8. The device ofclaim 6, wherein the active layer includes a GaAs_((1−x3))P_(x3) welllayer, where 1/9≦x3/(1−x3)≦¼.
 9. A method for manufacturing asemiconductor laser device, the method comprising: forming an n-typeclad layer; forming a first p-type clad layer; forming a ridge stripeincluding a second p-type clad layer formed into a ridge stripe shape onthe opposite surface of the first p-type clad layer from the n-type cladlayer; forming an active layer interposed between the n-type clad layerand the first p-type clad layer; and forming a current-blocking layerformed on side surfaces of the ridge stripe, wherein a first ridge widthof a surface of the second p-type clad layer existing on the same sideas the first p-type clad layers is greater than or equal to 3.0 μm andless than or equal to 4.5 μm, and a second ridge width of a surface ofthe second p-type clad layer existing at the opposite side from thefirst p-type clad layer is greater than or equal to 2.0 μm, wherein thesemiconductor laser device is a three-time-grown semiconductor laserdevice manufactured by forming a p-type contact layer after thecurrent-blocking layer is formed, wherein the current-blocking layer isformed of an n-type (Al_(x4)Ga_((1−x4)))_(0.51)In_(0.49)P (0≦x4≦1)layerthat has a composition satisfying an inequality, 0.7≦x4≦0.9, and whereinthe n-type clad layer, the first p-type clad layer and the second p-typeclad layer are formed of a (Al_(x1)Ga _(1−x1)))_(0.51)In_(0.49)P layerthat has a composition where x1>0.7.
 10. The method of claim 9, whereinthe current-blocking layer has a thickness of greater than or equal to300 nm and less than or equal to 450 nm.
 11. The method of claim 9,wherein the first p-type clad layer has a thickness of greater than orequal to 300 nm and less than or equal to 400 nm.
 12. The method ofclaim 9, wherein one or more end surface window structures for expandinga band gap of the active layer are formed in one or more end surfaceportions of a laser resonator.
 13. The method of claim 9, wherein theactive layer includes a GaAs_((1−x3))P_(x3) well layer, where1/9≦x3/(1−x3)≦¼.